Real-time digital x-ray imaging apparatus

ABSTRACT

An x-ray diagnostic apparatus and methods performs Real-Time Digital Radiography with particular application in dental x-ray imaging modalities, such as Orthopantomography, Scannography, Linear Tomography and Cephalography, by using a versatile and modular electronic unit, featuring ultra fast computation capability to serve diversified image sensor typology and scanning modality. In Digital Orthopantomography and Scannography, a plurality of tomographic images at different depths of the jaw can be generated, based on the pre-selection made by the user interface. The image processing unit utilizes for the tomo-synthesis of the diagnostic image an accurate and economic digital simulator of the radiographic film speed, including a digital frequency synthesizer fed with film cassette speed digital input and high resolution clock signal, ensuring accurate and reproducible phase continuity of the output frequency signal. It also introduces an automatic adaptation of the frame acquisition rate in frame transfer mode, based on the actual speed of the cassette unit. By this method the dynamic of the exposure signal is reduced, and a better optimization of the signal response of the x-ray detector is achieved.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of application Ser. No. 11/345,465filed Feb. 1, 2006, which is a Continuation of application Ser. No.10/205,257 filed Jul. 25, 2002, now U.S. Pat. No. 7,016,461, whichclaims the benefit of Provisional Application 60/307,627 filed on Jul.25, 2001.

BACKGROUND OF THE INVENTION

Orthopantomography, Scannography, Linear Tomography and Cephalographyare complementary radiographic techniques, often combined in a singleequipment, of widespread use in dental radiology to obtain respectivelya comprehensive survey of the maxillo-facial complex, tomographic viewsof selected anatomical districts under transversal or axial projections,and cranial views under multiple projections, supporting the diagnosisin the dental prevention, restoration and follow up.

Orthopantomography aims to produce a radiographic image of a curvedplane approximating the patient jaws, with blurring of the anatomicalstructures laying outside a narrow layer around the predesignated curvedplane, by using the relative movement of the radiographic film versusthe rotation of the x-ray source to generate the layer forming effect.

Scannography has a layer forming process similar to Orthopantomography,where the object is typically laying on a flat plane. It is practicallyused to produce axial or transverse views of specific anatomicaldistricts, such as the jaw, the joints and the sinus.

Linear Tomography is an alternative technique, using the classic lineartomographic layer forming projection. It is practically used to produceaxial or transverse views of specific anatomical districts in the jaw.

Cephalography is a stationary radiographic technique, aiming to produceradiographic images of the cranial complex under various projections,with minimum magnification and geometrical distortion.

For all radiographic modalities the real-time digital x-ray imageacquisition is nowadays a more and more interesting option, allowingremoval of the film processing and related chemicals, by takingadvantage of the improved performances and reduced costs provided by themodern image sensor technology.

Prior art (U.S. Pat. No. 4,188,537) describes apparatus and methods inwhich Realtime Digital Panoramic Radiography is implemented by an arrayof multiple detectors, or a vertical scanning single detector, wherevertical lines are acquired in synchronisation with the rotationmovement, so generating and displaying a panoramic image. This solutionis deficient, as it is lacking the layer forming effect.

Other prior art (U.S. Pat. No. 4,878,234) describes apparatus andmethods in which Real-time Digital Panoramic Radiography is implementedby CCD image sensors where vertical lines in the image zone are clockedout in the not-illuminated storage zone, by a frequency simulating thespeed of the moving x-ray film in the conventional Dental PanoramicTomography.

In other prior art arrangements (U.S. Pat. No. 4,823,369) Real-timeDigital Panoramic Radiography is implemented by x-ray image detectors,preferably consisting of amorphous silicon, where complete framescorresponding to the active area are acquired at sufficiently fastfrequency and adjacent frames are added as a function of time, either bypre-processing in order to obtain the panoramic image on one selectedlayer, or by storing in memory and later processing, so giving thepossibility of multiple layer reconstruction.

Further prior art arrangement (U.S. Pat. No. 4,995,062) describesapparatus and methods in which Real-time Digital Panoramic Radiographyis implemented by CCD image sensors where different vertical lines aredriven with different clock frequency so simultaneously obtaining aplurality of tomograms at different depths of the jaw.

Another prior art arrangement (U.S. Pat. No. 5,195,114) describesapparatus and methods in which Real-time Digital Panoramic Radiographyis accomplished by an X-ray image detection system, typically based on asignal intensifier tube camera (SIT), where video signal is acquired andstored in a storage unit (such as video tape recorder), and framedigital data are lately derived by A/D conversion and processedselecting frame interval and shift depending on the movement speed ofthe target, to digitally form the panoramic image of given tomographiclayers. This arrangement is limited in the video rate acquisition, anddoes not provide enough resolution for adequate panoramic imagereconstruction. The process is also time consuming and, in case ofdigital frame storage, would require huge amount of memory.

More recent prior art arrangement (EP 0 673 623) describes apparatus andmethods in which Real-time Digital Panoramic Radiography is implementedby X-ray detection system having an area coincident with thecross-section area of the X-ray and so requiring only one narrow slitX-ray diaphragm located on the X-ray source. By this arrangement thePanoramic image reconstruction is accomplished either by frameacquisition, with intermediate frame storage (memory consuming option)or with immediate frame processing (less memory consuming option), or bythe TDI method: in the first case for adequate layer formation the frameresolution must be chosen in a way to ensure that each point of thefinal reconstructed image is represented in more positionally shiftedimages (preferably five or more); in the second case (even less memoryconsuming) the image is directly integrated and formed on the X-raydetector, by controlling the clock sequence in a way to ensure that theprojected image of a point within the sharp layer of the object will berepresented by the same spatial position in the final reconstructedpanoramic image.

In Digital Panoramic Radiography, the following desirable features areapplicable:

-   -   To be able to generate simultaneously a plurality of panoramic        tomograms at different depths of the jaw.    -   To have an accurate, reproducible and inexpensive method of        simulating the speed of the x-ray detector (the radiographic        film). This information is necessary for the layer forming        processing required in the tomosynthesis of the panoramic image.    -   In the case where full frame acquisition is used, to have a        method to adapt to the varying dynamic of the exposure signal in        a way to optimise the signal response of the detector in terms        of signal to noise ratio.

Both in Real-time Digital Panoramic Radiography, Transversal Tomographyand Cephalography it is another desirable feature to have a commonelectronic hardware capable of serving with efficient and fast responsex-ray image sensors of various kind and structure and different scanningmethods such as TDI or frame transfer.

The purpose of this invention is to advantageously offer technicallyefficient and economic solution to all the desirable features above.

SUMMARY OF THE INVENTION

The object of the invention is a x-ray apparatus and methods capable ofperforming Real-time Digital Radiography with particular application inOrthopantomography, Scannography, Linear Tomography and Cephalography.

In Digital Orthopantomography and Scannography, the apparatus of theinvention will implement the following innovating features:

-   -   Simultaneous generation of a plurality of panoramic tomograms at        different depths of the jaw.    -   Digital simulation of the speed of the x-ray detector (the        radiographic film), by a frequency modulated signal directly        synthesized under microprocessor control, providing accurate        reproduction of the motor phase signal with phase continuity        control and motion direction sensing.    -   In the case where full frame acquisition is used, automatic        adaptation of the frame acquisition frequency to the actual        speed of the cassette unit. By this method the dynamic of the        exposure signal is reduced, and a better optimization of the        signal response of the x-ray detector is achieved.

In Real-time Digital Panoramic Radiography, Transversal Tomography andCephalography the apparatus will use an innovative common electronichardware and software solution, capable of serving with efficient andfast response x-ray image sensors of various kind and structure anddifferent scanning methods such as TDI or frame transfer.

The invention is particularly advantageous in dental radiography, wherethe outlined features find immediate application, but it could also beadvantageously employed in other medical and non-medical applicationshaving similar requirements.

Here following is a description in greater detail of the invention,based on the exemplary embodiment illustrated in the attached drawings.

DESCRIPTION OF DRAWINGS AND TABLES

FIG. 1 is a diagram showing an exemplary system dedicated to dentalapplication.

FIG. 2 is a flow chart illustrating the main apparatus functional units.

FIG. 3 is a block diagram illustrating the main apparatus functionalunits in cascade architecture.

DETAILED DESCRIPTION

The system illustrated in FIG. 1 is a typical dental x-ray diagnosticsystem performing Real-time Digital Radiography in Orthopantomography,Scannography, Linear Tomography and Cephalography.

For those skilled in the art, it is intended that:

Orthopantomography is a narrow beam scanning technique aiming toreproduce in a single radiographic view the whole or part of a curveplane approximating the patient jaw, using layer forming methods bywhich the points laying in the target plane are reproduced on the samepoint of the radiographic image, while points laying outside the targetplane are blurred out.

Scannography is a narrow beam scanning technique aiming to reproduce ina single radiographic view the whole or part of a flat planeapproximating specific anatomical regions (such as the jaw, the joints,the sinus), using layer forming methods by which the points laying inthe target plane are reproduced on the same point of the radiographicimage, while points laying outside the target plane are blurred out.

Linear tomography is a wider beam radiographic technique, using theclassic linear tomographic layer forming projection, where by thecombined movement of x-ray source and x-ray imager around the object,only the points laying in the target plane are reproduced on the samepoint of the radiographic image, while points laying outside the targetplane are blurred out.

Cephalography is a stationary radiographic technique, where the cranialcomplex is exposed under various projections, with minimum magnificationand geometrical distortion.

With reference to FIG. 1:

The x-ray source 1 is aligned with the image receptor 2 (the x-rayimager) by a suitable connecting arm for panoramic radiography andtomography.

The x-ray source 1 can also be tilted and aligned with the imagereceptor 3 (the x-ray imager) by another connecting arm for performingcephalographic exposure.

Eventually a suitable translation mechanism will allow image receptor 2to be relocated in position of image receptor 3 for performingcephalography with a unique x-ray imager.

The system is capable of performing orbital projections around thepatient skull with simultaneous acquisition, by the x-ray detector, ofthe imaging data necessary for the reconstruction of the diagnosticimage.

Depending on the applicable technique, the system will use a scanningprocess, with or without layer forming processing, to build up thediagnostic image in panoramic radiography and in transversal or axialtomography.

The Image Processing Unit 4 (IPU) performs the diagnostic imageprocessing and reconstruction. In case of Orthopantomography orScannography it will use the cassette motor control simulated signal asan input to modulate the frame rate acquisition.

The IPU is made of basic blocks, typically associated to correspondingblocks of the x-ray imager, consisting of: the shared data bus, the A/Dconverter, the FIFO Registry, the Full Adder, the Control Logic, theCassette Speed Simulator, The Sensor Integration Control, and the ImageMemory.

Here following is a description in greater detail of the functionalunits composing the apparatus of the invention, which also makesreference to the system block diagram in FIG. 2 and FIG. 3.

The X-ray imager is intended as the x-ray image sensor of any kind,providing either intermediate conversion of x-rays to light (for exampleby a suitable scintillator layer, with or without fiber optics coupling)or providing direct conversion of x-rays to electric charge (for exampleby adopting direct x-ray detection layers and bonding technique to thereadout layer).

The read out section of the sensor can be a CCD device, controlled byphase control signals generated by the Control Logic, and operated ineither of the following two modes:

-   -   Full Frame, where the entire image is transported line by line,        by charge transfer during irradiation, to the readout registers        where the pixel readout is done through the output amplifier.    -   Frame Transfer, where the entire image is first quickly        transported during irradiation to the storage section (obscured        from irradiation), and then the entire frame is read out as        above.

Or it can be a CMOS device, where the control signals generated by theControl Logic sequence, by column and rows counters, the addressing andread out of the matrix pixels in whatever arrangement is foreseen (byline, by column, by windowing, etc.).

The A/D converter receives as an input the video out signal generated bythe x-ray sensor and converts it into digital form, with a resolution,which typically ranges from 8 to 16 bit, synchronized with the pixelrate by the Control Unit. The digital pixel data are readable throughthe parallel data bus.

The parallel data bus is the data channel through which the pixel dataare exchanged between the A/D converter (out only), the FIFO registry(in and out), the Full Adder (in and out) and the Image Memory (inonly).

The whole data bus operation is governed by the Control Logic.

The Control Logic contains all the programmable logic to generate thephase sequence and/or addressing for the x-ray sensor and the controlsignals to govern the enable and data exchange between the FIFORegistry, the Full Adder and the Image Memory through the data bus.

The FIFO Registry represents the temporary storage device, where thepixel data are stored, processed and shifted before transfer to theimage memory.

The dimension and organization of the FIFO Registry depends on theoperating mode and structure of the x-ray sensor acquisition (by frame,by column, by pixel window, etc.).

The Full Adder is an arithmetic unit performing add operation on theFIFO data.

The Cassette Speed Simulator (CSS), is the functional unit dedicated tothe synthesis of the frequency signal simulating the speed of the filmcassette.

The input is the digital data referred to the cassette speed for a givenprojection. Such digital data represent the actual speed over a timeinterval (a typical interval is 20 msec).

The simulator operates on the base of the system clock frequency(typically 48 MHz) and in response to the input velocity data (withminimum 12 bit resolution) directly synthesizes the output frequencysimulating the cassette drive speed, ensuring phase continuity operationby the mechanism of Direct Digital Synthesis (DDS) with phaseaccumulation, as well known to those skilled in the art.

Additionally the DDS synthesizer can be fashioned in a “Multi Channel”arrangement, in order to provide an economic solution for thesimultaneous simulation of multiple speed profiles. For example it maybe advantageously used to generate more cassette speed profiles onprojections referred to different positions of the layer in focus.

The frequency output signal can be immediately utilized by the ControlLogic to govern the shift operation in the TDI mode, directly on thesensor, or in the pseudo-TDI mode during processing on the FIFORegistry.

The Sensor Integration Control is a functional unit receiving as aninput the current cassette speed, and providing as an output thecorresponding varying duration of the integration time on the sensor.This output is used by the Control Logic to govern the frame acquisitionrate and the consequent data processing.

This is particularly useful in case of frame acquisition, where it isnot wise to perform frame acquisition always at maximum rate. Especiallyin phases of the projection where the speed is lower the frameacquisition rate can be reduced, still maintaining adequate frameresolution in view of image reconstruction.

In fact in practical applications the film speed reduction usuallyaccompanies to reduced irradiation, so intrinsically giving a stabilizedlevel of the exposure rate on the sensor. Therefore the adjustment ofthe sensor integration time in dependence of the cassette speed leads toa reduced dimensioning of the x-ray exposure dynamic of the imagesensor, so favoring in general an improved signal to noise response ofthe same sensor. In a typical application the Sensor Integration Time(SIT) may relate with the Actual Cassette Speed (ACS) as follows: SIT(s)= 1/10*ACS (mm/s)

The Image Memory is the storage device where the image data aredeposited after processing. Typically the image data are stored columnby column in adjacent positions, up to form the complete image.

Eventually more image memories can be used at the same time,corresponding to images generated from projections referred to differentpositions of the layer in focus.

As a particular application of the general arrangement described above,the more general parallel data bus structure can conveniently beimplemented using the simplified structure of FIG. 3, where the FullAdder and the FIFO are arranged in “cascade architecture”.

The “cascade architecture” may either be embedded in the hardware, suchas in the case of using FPGA type Programmable Logic Devices, orimplemented in the software micro code, such as in the case of usingDigital Signal Processor devices.

Based on the functional units above, the methods of this invention willbe based on various operating steps of the IPU, depending on theradiographic modality chosen, the sensor type and the foreseenacquisition mode.

In Orthopantomography and Scannography the following cases apply:

-   -   (a) Case of a CCD sensor Full Frame, with direct integration and        TDI operation on-the-sensor.

The signal is directly integrated on the sensor, while the speedsimulated signal is used to govern the column shift operation on thesensor.

The last column is shifted in the readout register and it is readoutpixel by pixel through the A/D converter into the FIFO Registry.

On termination the entire column is transferred from the FIFO Registryto the Image Memory, adjacent to the previously acquired column.

-   -   (b) Case of CCD sensor driven in Frame Transfer, with pseudo-TDI        image reconstruction.

At regular intervals, as dictated by the Control Logic under input fromthe SIC, the entire image is integrated and then quickly transportedduring irradiation to the storage section (obscured from irradiation).

Then pixel by pixel the entire frame is read out into the FIFO Registry.Depending on the sequence dictated by the Control Logic in response tothe CSS, the individual pixel is added to the corresponding pixel in theFIFO Registry.

On termination the columns of the FIFO Registry are shifted, and thelast column is moved into the Image Memory, adjacent to the previouslyacquired column.

-   -   (c) Case of CMOS sensor, with pseudo-TDI image reconstruction.

At regular intervals, as dictated by the Control Logic under input fromthe SIC, the entire image is scanned with sequential pixel addressingand read out, by rows or by columns, eventually applying a useful windowwithin the sensor active area.

Depending on the sequence dictated by the Control Logic in response tothe CSS, the individual pixel is added to the corresponding pixel in theFIFO Registry.

On termination all the columns of the FIFO Registry are shifted, and thelast column of the Registry is moved into the Image Memory, adjacent tothe previously acquired column.

In Linear Tomography the CSS and SIC are not active. The following casesapply:

(a) Case of a CCD Sensor Full Frame, with Direct Integrationon-the-Sensor.

The signal is directly integrated on the sensor during the whole time ofirradiation. On termination the image is shifted column by column to thereadout register and is readout pixel by pixel through the A/D converterinto the FIFO Registry.

On termination the entire column is transferred from the FIFO Registryto the Image Memory, adjacent to the previously acquired column.

(b) Case of CCD Sensor Driven in Frame Transfer.

At regular intervals, as dictated by the frame acquisition rate from theControl Logic, the entire image is integrated and then quicklytransported during irradiation to the storage section (obscured fromirradiation).

Then pixel by pixel the entire frame is added to the corresponding pixelin the FIFO Registry, so building up the image by digital integration.

On termination the entire image is moved, by column shifting, from theFIFO Registry into the Image Memory.

(c) Case of CMOS Sensor, with Direct Integration on-the-Sensor.

The signal is directly integrated on the sensor during the whole time ofirradiation. On termination the sensor is scanned pixel by pixel(eventually within a specified window) and the image data are directlytransferred to the Image Memory.

(d) Case of CMOS Sensor Driven in Frame Transfer.

At regular intervals, as dictated by the Control Logic, the entire imageis scanned with sequential pixel addressing and read out, by rows or bycolumns, eventually applying a useful window within the sensor activearea.

Then pixel by pixel the entire frame is added to the corresponding pixelin the FIFO Registry, so building up the image by digital integration.

On termination the entire image is moved, by column shifting, from theFIFO Registry into the Image Memory.

In Cephalography, a scanning method is applied, where the rigid couplingof x-ray source and sensor is translated either horizontally orvertically across the object, and the sensor is exposed with a narrowcollimated x-ray beam.

The CSS and SIC are not active. The following cases apply:

(a) Case of a CCD Sensor Full Frame, with Direct Integrationon-the-Sensor.

The signal is directly integrated on the sensor. The irradiation iscontinuous, while the sensor columns are shifted by the Control Logic ata speed such to ensure the coincidence on the same column of theprojection of the same object point laying in the mid sagittal plane ofthe patient head.

The last column is shifted to the readout register and is readout pixelby pixel through the A/D converter into the FIFO Registry.

On termination the entire column is transferred from the FIFO Registryto the Image Memory, adjacent to the previously acquired column.

(b) Case of CCD Sensor Driven in Frame Transfer.

At regular intervals, as dictated by the frame acquisition rate from theControl Logic, the entire image is integrated and then quicklytransported during irradiation to the storage section (obscured fromirradiation).

Then pixel by pixel the entire frame is added to the corresponding pixelin the FIFO Registry, so building up the image by digital integration.

The frame in the FIFO Registry is also shifted by the Control Logic at aspeed such to ensure the coincidence on the same column of theprojection of the same object point laying in the mid sagittal plane ofthe patient head.

The last shifted column of the FIFO Registry is moved into the ImageMemory, adjacent to the previously acquired column.

As alternative method, applicable in case of higher intensity pulsedexposure sequence, the entire image is integrated during one exposureflash and then, after the exposure, it is quickly transported to thestorage section.

The entire frame is then readout and transferred in the FIFO Registry,so building up one vertical strip of the image.

The whole or part of the frame in the FIFO Registry is therefore moved,by column shifting, into the Image Memory, adjacent to the previouslyacquired strip.

The above sequence is repeated with the next exposure flash taking placein the next adjacent position of x-ray source and sensor.

(c) Case of CMOS Sensor Driven in Frame Transfer.

At regular intervals, as dictated by the frame acquisition rate from theControl Logic, the entire image is integrated and then quickly readoutpixel by pixel through the A/D converter.

The readout frame is added to the corresponding pixel in the FIFORegistry, so building up the image by digital integration.

The frame in the FIFO Registry is also shifted by the Control Logic at aspeed such to ensure the coincidence on the same column of theprojection of the same object point laying in the mid sagittal plane ofthe patient head.

The last shifted column of the FIFO Registry is moved into the ImageMemory, adjacent to the previously acquired column.

As alternative method, applicable in case of higher intensity pulsedexposure sequence, the entire image is integrated during one exposureflash and then, after the exposure, it is quickly readout andtransferred in the FIFO Registry, so building up one vertical strip ofthe image.

The whole or part of the frame in the FIFO Registry is therefore moved,by column shifting, into the Image Memory, adjacent to the previouslyacquired strip.

The above sequence is repeated with the next exposure flash taking placein the next adjacent position of x-ray source and sensor.

It is an advantage of the present invention that by simple replicatingthe above FIFO Registry, the CSS, the SIC and the destination ImageMemory, image reconstruction on more layers in Orthopantomography andScannography can be easily achieved.

It would be in fact very useful, for example, that the clinician can preselect by the user interface more layers around the principal layer infocus and the apparatus can instantly process and generate on theequipment the corresponding diagnostic images ready for transfer to ahost computer, without need of huge amount of memory for storage of allthe acquired frames, or huge data transfer rates for transfer of thewhole series of frames to the host computer.

It is prerequisite that the electronic structure above providessufficient processing speed to accomplish with the required computationload.

For example considering a cassette speed range up to 30 mm/s, astypically used in Orthopantomography, and a pixel size of 0.1 mm, frameacquisition rates up to 600 f/s shall be possible.

In case of multiple layer reconstruction, the electronics shall be fastenough to process each acquired frame for each of the various layersforeseen.

In case of a 30,000 pixels sensor block with 3 layers reconstruction anoverall frequency of 54 MHz is required.

It is another advantage of the present invention the possibility toeasily accomplishing with projections having reverse rotation movement,provided that the used sensor allows for right and left readout of thepixel matrix.

This is particularly useful in the case where symmetric projections areachieved by simple replicating the same projection digital structurewith reversed rotation, so allowing reduction of the memory spacenecessary for projection data storage.

The present invention provides a dental x-ray diagnostic apparatusperforming Real-time Digital Radiography in various modalities such asOrthopantomography, Linear Tomography, Scannography and Cephalography.It includes (referring to FIG. 1):

-   -   A. An x-ray source 1, rigidly connected with an x-ray imager 2,        providing x-ray generation, equipped with collimating means to        provide limitation of the radiation incident on the x-ray        imager.    -   B. An x-ray imager 2, preferably rigidly connected and aligned        with the x-ray source 1, and being electrically coupled to a        suitable Image Processing Unit 3.    -   C. A cinematic unit 4, allowing execution of orbital movements        of x-ray source 1 and x-ray imager 2 around the patient skull,        allowing projections as required for Orthopantomography,        Scannography and Tomography.    -   D. A mechanism to allow alignment of the x-ray source with        another x-ray imager 5, for performing Cephalography, or        alternatively allowing relocation of the same x-ray imager in        the position 5 for Cephalography.    -   E. An Image Processing Unit (IPU) 3, performing the x-ray imager        control and the image processing functions, composed by the        following functional units (refer to FIG. 2 and FIG. 3):

(a) The Control Logic

Functional unit containing all the programmable logic to generate thephase sequence and/or addressing for the x-ray imager and the controlsignals to govern the enable and data exchange between the FIFORegistry, the Full Adder and the Image Memory through the data bus.

(b) The A/D Converter

Functional unit performing the analogue to digital conversion of thevideo out signal generated by the x-ray imager, synchronized with thepixel rate by the Control Logic. The digital pixel data output isreadable through the parallel data bus.

(c) The Parallel Data Bus

The data channel through which the pixel data are exchanged between theA/D converter (out only), the FIFO registry (in and out), the Full Adder(in and out) and the Image Memory (in only).

The whole data bus operation is governed by the Control Logic.

(d) The FIFO Registry

Functional unit representing the temporary storage device, where thepixel data are stored, processed and shifted before transfer to theimage memory.

The dimension and organization of the FIFO Registry depends on theoperating mode and structure of the x-ray sensor acquisition (by frame,by column, by pixel window, or the like).

(e) The Full Adder.

Functional unit performing add operation on the FIFO data.

(f) The Cassette Speed Simulator (CSS).

Functional unit dedicated to the synthesis of the frequency signalsimulating the speed of the film cassette.

The input is the digital data referred to the cassette speed for a givenprojection. Such digital data represent the actual speed over a timeinterval (a typical interval is 20 msec).

The simulator operates on the base of the system clock frequency(typically 48 MHz) and in response to the input velocity data (withminimum 12 bit resolution) directly synthesizes the output frequencysimulating the cassette drive speed, ensuring phase continuity operationby the mechanism of Direct Digital Synthesis (DDS) with phaseaccumulation, conventional and known to those skilled in the art. Thefrequency output signal can be substantially immediately utilized by theControl Logic to govern the shift operation in the TDI mode, directly onthe sensor, or in the pseudo-TDI mode during processing on the FIFORegistry.

(g) The Sensor Integration Control (SIC)

Functional unit receiving as an input the current cassette speed, andproviding as an output the corresponding varying duration of theintegration time on the sensor. This output is used by the Control Logicto govern the frame acquisition rate and the consequent data processing.

This is particularly useful in case of frame acquisition, where it isnot wise to perform frame acquisition always at maximum rate. Especiallyin phases of the projection where the speed is lower the frameacquisition rate can be reduced, still maintaining adequate frameresolution in view of image reconstruction.

In practical applications the film speed reduction usually accompaniesreduced irradiation, thereby intrinsically providing a stabilized levelof the exposure rate on the sensor. Therefore the adjustment of thesensor integration time in dependence of the cassette speed leads to areduced dimensioning of the x-ray exposure dynamic of the image sensor,so favoring in general an improved signal to noise response of the samesensor. In a typical application the Sensor Integration Time (SIT) mayrelate with the Actual Cassette Speed (ACS) as follows: SIT (s)=1/10*ACS (mm/s)

(h) The Image Memory

It is the storage unit where the image data are deposited afterprocessing. Typically the image data are stored column by column inadjacent positions, up to form the complete image.

Eventually more image memories can be used at the same time,corresponding to images generated from projections referred to differentpositions of the layer in focus.

The X-ray imager 2 is an x-ray image sensor of any conventional design,providing either intermediate conversion of x-rays to light (for exampleby a suitable scintillator layer, with or without fiber optics coupling)or providing direct conversion of x-rays to electric charge (for exampleby adopting a direct x-ray detection layer and bonding technique to thereadout layer).

The X-ray imager 2 may have a read out section made of a CCD device,controlled by phase control signals generated by the Control Logic, andoperated in Full Frame mode, where the entire image is transported lineby line, by charge transfer during irradiation, to the readoutregisters, where the pixel readout is done through the output amplifier.

The X-ray imager 2 may also be an x-ray image sensor having the read outsection made of a CCD device, controlled by phase control signalsgenerated by the Control Logic, and operated in Frame Transfer mode,where the entire image is first quickly transported during irradiationto the storage section (obscured from irradiation), and then the entireframe is transported line by line, by charge transfer, to the readoutregisters, where the pixel readout is done through the output amplifier.It may also be an x-ray image sensor having the read out section made ofa CMOS device, where the control signals are generated by the ControlLogic sequence, by column and rows counters, the addressing and read outof the matrix pixels under any of several conventional arrangements,including for example, by line, by column, by windowing, and the like.

The IPU functional structure is preferably replicated, two or moretimes, allowing in Orthopantomography and Scannography simultaneousimage reconstruction on more layers. It is preferably accompanied withthe control given to the user to preselect by a suitable user interface,analog or digital, multiple layers around the principal layer in focus.

It is also possible according to the present invention, to perform imagereconstruction in Orthopantomography and Scannography both withclockwise and counterclockwise orbital movements, either by using CCDsensors with dual readout register structure, or by using FIFO Registrywith bi-directional shift operation.

According to one embodiment of the invention, a “Multi Channel”configuration of the CSS functional unit is advantageously used, wheremultiple profiles are simulated at the same time, corresponding forexample to cassette speeds on projections referred to differentpositions of the layer in focus.

As a particular application of the more general parallel data structure,the Full Adder and the FIFO according to the invention, may be organizedin a “cascade architecture” either embedded in the hardware, such as inthe case of using FPGA type Programmable Logic devices, or implementedin the software micro code, such as in the case of using Digital SignalProcessor devices.

A method for operating a dental x-ray diagnostic apparatus performingRealtime Digital Radiography in Orthopantomography and Scannography,comprises the steps of:

-   -   Irradiating the patient skull during the orbital movement of        x-ray source and x-ray imager.    -   Controlling by the 055 signal the column shift operation on the        x-ray imager.    -   Shifting the last column in the readout register, and reading it        out pixel by pixel through the A/D converter into the FIFO        Registry.    -   On termination transferring the entire column from the FIFO        Registry to the Image Memory, adjacent to the previously        acquired column, so building up the whole diagnostic image.

This inventive method is particularly applicable to x-ray imagers havinga readout section made of a CCD sensor operated in Full Frame, withdirect integration and TDI operation on-the-sensor.

A method for operating a dental x-ray diagnostic apparatus performingReal-time Digital Radiography in Orthopantomography and Scannography,comprises the steps of:

-   -   Irradiating the patient skull during the orbital movement of        x-ray source and x-ray imager.    -   Controlling at regular intervals, as dictated by the Control        Logic under input from the SIC, the frame integration and the        quick frame transfer during irradiation to the storage section        (obscured from irradiation).    -   Reading the entire frame out from the storage section through        the A/D converter, and adding it, pixel by pixel, to the FIFO        Registry.    -   Shifting the frame columns in the FIFO Registry, based on the        sequence dictated by the Control Logic in response to the CSS.    -   Transferring the last shifted column from the FIFO Registry to        the Image Memory, adjacent to the previously acquired column, so        building up the whole diagnostic image.

This method is particularly applicable to x-ray imagers having a readoutsection made of a CCD sensor operated in Frame Transfer mode, withpseudo-TDI image reconstruction.

A method for operating a dental x-ray diagnostic apparatus performingReal-time Digital Radiography in Orthopantomography and Scannography,comprises the steps of:

-   -   irradiating the patient skull during the orbital movement of        x-ray source and x-ray imager.    -   Controlling at regular intervals, as dictated by the Control        Logic under input from the SIC, the frame integration and quick        readout during irradiation through the A/D converter, and the        frame adding, pixel by pixel, to the FIFO Registry.    -   Shifting the frame columns in the FIFO Registry, based on the        sequence dictated by the Control Logic in response to the OSS.    -   Transferring the last shifted column from the FIFO Registry to        the Image Memory, adjacent to the previously acquired column, so        building up the whole diagnostic image.

This method is particularly applicable to x-ray imagers having a readoutsection made of a CMOS sensor operated in Frame Transfer mode, withpseudo-TDI image reconstruction.

A method for operating a dental x-ray diagnostic apparatus performingReal-time Digital Radiography in Linear Tomography, comprising the stepsof:

-   -   Irradiating the patient skull during the orbital movement of        x-ray source and x-ray imager.    -   On termination of irradiation, shifting the whole frame, column        by column, to the readout register.    -   Reading out, for each shifted column, the readout register        through the A/D converter, and moving it, pixel by pixel, to the        FIFO Registry.    -   Moving the last readout column from the FIFO Registry to the        Image Memory, adjacent to the previously acquired column, so        building up the whole diagnostic image.

This method is particularly applicable to x-ray imagers having a readoutsection made of a CCD sensor operated in Full Frame mode.

A method for operating a dental x-ray diagnostic apparatus performingReal-time Digital Radiography in Linear Tomography, comprises the stepsof:

-   -   Irradiating the patient skull during the orbital movement of        x-ray source and x-ray imager.    -   On termination of irradiation, reading out the whole frame        through the A/D converter, and moving it, pixel by pixel, to the        FIFO Registry.    -   Moving the whole frame, by column shifting, from the FIFO        Registry to the Image Memory.

This method is particularly applicable to x-ray imagers having a readoutsection made of a CMOS sensor with full integration on-the-sensor.

A method for operating a dental x-ray diagnostic apparatus performingReal-time Digital Radiography in Linear Tomography, comprising the stepsof:

-   -   Irradiating the patient skull during the orbital movement of        x-ray source and x-ray imager.    -   Controlling at regular intervals, as dictated by the Control        Logic, the frame integration and the quick frame transfer during        irradiation to the storage section (obscured from irradiation).    -   Reading the entire frame out from the storage section through        the A/D converter, and adding it, pixel by pixel, to the FIFO        Registry.    -   On termination of irradiation, moving the whole frame from the        FIFO Registry to the Image Memory.

This method is particularly applicable to x-ray imagers having a readoutsection made of a CCD sensor operated in Frame Transfer mode.

A method for operating a dental x-ray diagnostic apparatus performingReal-time Digital Radiography in Linear Tomography, comprising the stepsof:

-   -   Irradiating the patient skull during the orbital movement of        x-ray source and x-ray imager.    -   Controlling at regular intervals, as dictated by the Control        Logic, the frame integration and the frame readout, pixel by        pixel, through the A/D converter. Eventually, a useful window        may be applied within the sensor active area.    -   Adding the readout data, pixel by pixel, to the FIFO Registry,        so building up the image by digital integration.    -   On termination of irradiation, moving the whole frame from the        FIFO Registry to the Image Memory.

This method is particularly applicable to x-ray imagers having a readoutsection made of a CMOS sensor driven in Frame Transfer mode.

A method for operating a dental x-ray diagnostic apparatus performingReal-time Digital Radiography in Cephalography, comprises the steps of:

-   -   Irradiating the patient skull under cephalographic projection,        while x-ray source and x-ray imager perform a linear scanning        movement.    -   Shifting the sensor columns, as dictated shifted by the Control        Logic, at a speed such to ensure the coincidence on the same        sensor column of the projection of the same object point laying        in the mid sagittal plane of the patient head.    -   Shifting of the last column in the readout register, and reading        out pixel by pixel through the A/D converter into the FIFO        Registry.    -   Moving the last readout column from the FIFO Registry to the        Image Memory, adjacent to the previously acquired column, so        building up the whole diagnostic image.

This method is particularly applicable to x-ray imagers having a readoutsection made of a CCD sensor operated in Full Frame mode.

A method for operating a dental x-ray diagnostic apparatus performingReal-time Digital Radiography in Cephalography, comprises the steps of:

-   -   Irradiating the patient skull under cephalographic projection,        while x-ray source and x-ray imager perform a linear scanning        movement.    -   At regular intervals, as dictated by the frame acquisition rate        from the Control Logic, integrating and quickly moving the frame        during irradiation to the storage section (obscured from        irradiation).    -   Reading the entire frame out from the storage section through        the A/D converter, and adding it, pixel by pixel, to the FIFO        Registry.    -   Shifting the frame columns in the FIFO Registry, as dictated by        the Control Logic, at a speed such to ensure the coincidence on        the same column of the projection of the same object point        laying in the mid sagittal plane of the patient head.    -   Moving the last shifted column from the FIFO Registry to the        Image Memory, adjacent to the previously acquired column, so        building up the whole diagnostic image.

This method is particularly applicable to x-ray imagers having a readoutsection made of a CCD sensor operated in Frame Transfer mode.

A method for operating a dental x-ray diagnostic apparatus performingReal-time Digital Radiography in Cephalography, comprising the steps of:

-   -   Irradiating the patient skull under cephalographic projection,        while x-ray source and x-ray imager perform a linear scanning        movement, where x-ray pulses are synchronized with the scanning        movement.    -   At intervals synchronized with the x-ray pulses by the Control        Logic, integrating and quickly moving the frame after        irradiation to the storage section (obscured from irradiation).    -   Reading the entire frame out from the storage section through        the A/D converter, and adding it, pixel by pixel, to the FIFO        Registry, so building up one vertical strip of the image.    -   Moving the whole or part of the frame in the FIFO Registry to        the Image Memory, adjacent to the previously acquired strip, so        building up the whole diagnostic image.    -   Repeating the above sequence with the next exposure flash,        taking place in the next adjacent position of x-ray source and        sensor.

This method is particularly applicable to x-ray imagers having a readoutsection made of a CCD sensor operated in Frame Transfer mode, used incombination with pulsed irradiation.

A method for operating a dental x-ray diagnostic apparatus performingReal-time Digital Radiography in Cephalography, comprising the steps of:

-   -   Irradiating the patient skull under cephalographic projection,        while x-ray source and x-ray imager perform a linear scanning        movement.    -   At regular intervals, as dictated by the frame acquisition rate        from the Control Logic, integrating and quickly reading out the        whole frame during irradiation through the A/D converter, and        adding it, pixel by pixel, to the FIFO Registry, so building up        the image by digital integration.    -   Shifting the frame columns in the FIFO Registry, as dictated by        the Control Logic, at a speed such to ensure the coincidence on        the same column of the projection of the same object point        laying in the mid sagittal plane of the patient head.    -   Moving the last shifted column from the FIFO Registry to the        Image Memory, adjacent to the previously acquired column, so        building up the whole diagnostic image.

This method is particularly applicable to x-ray imagers having a readoutsection made of a CMOS sensor operated in Frame Transfer mode.

A method for operating a dental x-ray diagnostic apparatus performingReal-time Digital Radiography in Cephalography, comprises the steps of:

-   -   Irradiating the patient skull under cephalographic projection,        while x-ray source and x-ray imager perform a linear scanning        movement, where x-ray pulses are synchronized with the scanning        movement.    -   At intervals synchronized with the x-ray pulses by the Control        Logic, integrating and, after the irradiation, quickly reading        out the entire frame, pixel by pixel, through the A/D converter        into the FIFO Registry, so building up one vertical strip of the        image.    -   Moving the whole or part of the frame in the FIFO Registry to        the Image Memory, adjacent to the previously acquired strip, so        building up the whole diagnostic image.    -   Repeating the above sequence with the next exposure flash,        taking place in the next adjacent position of x-ray source and        sensor.

This method is particularly applicable to x-ray imagers having a readoutsection made of a CMOS sensor operated in Frame Transfer mode, used incombination with pulsed irradiation.

By using any of these inventive methods, a user can preselect by theappropriate user interface more or multiple layers of interest aroundthe principal layer in focus and, having replicated the IPU functionalstructure, in Orthopantomography and Scannography simultaneous imagereconstruction on more layers is accomplished.

By using any of these inventive methods, via adequate adjustment by theControl Logic of the direction of the shift operation, either on CCDsensors with dual readout register structure, or on the FIFO Registry,the possibility is given to perform image reconstruction inOrthopantomography and Scannography both with clockwise andcounterclockwise orbital movements.

1. A dental x-ray diagnostic apparatus for performing real-time digitalradiography of a patient skull, comprising an x-ray source rigidlyconnected to an x-ray imager providing x-ray generation; said x-rayimager being electrically coupled to an image processing unit andallowing execution of orbital movements of said x-ray source and saidx-ray imager around the patient skull, allowing projections as requiredfor Orthopantomography, Scannography and Tomography.
 2. An apparatus asin claim 1, further comprising an alignment mechanism to allow alignmentof said x-ray source with a second x-ray imager for performingOephalography.
 3. An apparatus as in claim 1, wherein said x-ray imageris relocatable thereby allowing relocation of said x-ray imager in theposition for Oephalography.
 4. An image processing unit for performingx-ray imager control and image processing functions in a dental x-rayapparatus, comprising a control logic functional unit containingprogrammable logic to generate a phase sequence or addressing functionfor said x-ray imager and control signals to control the enable and dataexchange between a FIFO Registry, a Full Adder and an Image Memorythrough a data bus.
 5. A unit as in claim 4, further comprising afunctional converter for performing analogue to digital conversion of avideo out signal generated by an x-ray imager, synchronized with a pixelrate by said control logic.
 6. A unit as in claim 5, wherein digitalpixel data output is readable through a parallel data bus.
 7. A unit asin claim 6, wherein said parallel data bus is a data channel throughwhich pixel data is exchanged between said converter, said FIFOregistry, said Full Adder and said Image Memory.
 8. A unit as in claim7, wherein said FIFO Registry comprises a temporary storage device,wherein pixel data are stored, processed and shifted before transfer tosaid image memory.
 9. A unit as in claim 8, wherein said Full Adderperforms an add operation on FIFO data.
 10. A unit as in claim 9,further comprising a Cassette Speed Simulator (CSS).
 11. A unit as inclaim 10, wherein said CSS provides the synthesis of a frequency signalsimulating the speed of the film cassette.
 12. A unit as in claim 11,wherein digital data is referred to the cassette speed for a givenprojection, thereby representing the actual speed over a time interval.13. A unit as in claim 12, wherein said CSS operates on the base of asystem clock frequency and in response to input velocity data,synthesizes the output frequency simulating the cassette drive speed,ensuring phase continuity operation by Direct Digital Synthesis (DDS)with phase accumulation.
 14. A unit as in claim 13, further comprising asensor integration control (SIC) for receiving as an input the cassettespeed, and providing as an output the corresponding varying duration ofthe integration time on said sensor.
 15. A unit as in claim 14, whereinsaid output is used by said control logic to control a frame acquisitionrate.
 16. A unit as in claim 15, wherein said imager is an x-ray imagesensor providing conversion of x-rays to light or providing conversionof x-rays to an electric charge.
 17. A unit as in claim 16, wherein saidx-ray imager has a COD read out section controlled by phase controlsignals generated by said control logic.
 18. A unit as in claim 17,wherein said imager is operated in a full frame mode.
 19. A unit as inclaim 17, wherein said COD device is controlled by phase control signalsgenerated by said control logic.
 20. A unit as in claim 19, wherein saidimager is operated in a frame transfer mode.
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